This invention relates to treatments for vascular disease.
In our prior patent applications, Intracranial Stent and Method of Use, U.S. patent application Ser. Nos. 08/707,996 (Sep. 18, 1996) and 08/761,110 (Dec. 9, 1996), we disclosed numerous embodiments of stents and stent delivery systems which enable surgeons to place stents deep within the brain. The inventions described in our prior applications were developed with the goal of providing new and better therapies for certain types of vascular disease for which the present day therapies are widely regarded as inadequate. Vascular disease includes aneurysms which can rupture and cause hemorrhage, atherosclerosis which can cause the occlusion of the blood vessels, vascular malformation and tumors. Occlusion of the coronary arteries, for example, is a common cause of heart attack. Vessel occlusion or rupture of an aneurysm within the brain are causes of stroke. Tumors fed by intra-cranial arteries can grow within the brain to the point where they cause a mass effect. The mass and size of the tumor can cause a stroke or the symptoms of stroke, requiring surgery for removal of the tumor or other remedial intervention.
Stents have not previously been used for aneurysms of the blood vessels in the brain. The vessels in the brain likely to develop stenosis, aneurysms, AVM""s and side branches requiring occlusion have diameters of about 1 mm to 5 mm, and can be accessed only via highly tortuous routes through the vascular system. Instead, surgical clipping, resection, complete occlusion with acrylic-based adhesives (super glue) or small balloons (thereby intentionally occluding the downstream portion of the blood vessel and any portion of the brain supplied by that portion), stuffing with foreign objects, etc. have been used. In a method of current interest, small coils are stuffed into the aneurysm via a catheter. One such small coil is known as the Guglielmi Detachable Coil or GDC. After placement of a few coils, which partially obstruct blood flow in the aneurysm, the blood clots or fibrous matter forms within the sac. This technique has reportedly resulted in clots and coils falling out of the sac, and the technique is not used on wide-neck aneurysms. Aneurysm clipping, in which the skull is opened and the brain dissected to expose the outside of the aneurysm, followed by placement of clips at the base of the aneurysm, is also an option for treatment. However, these techniques do not always effect an immediate and complete seal of the aneurysm from the high pressure of the circulatory system, and rupture, leakage and deadly complications occur. Aneurysm rupture and bleeding during surgical clipping and shortly after the clip placement is a significant problem and add difficulty to the procedure. Examples of the problems inherent in the use of both GDC""s and aneurysm clips are illustrated in Civit, et al., Aneurysm Clipping After Endovascular Treatment With Coils, 38 Neurosurgery 955 (May 1996) which reports that several patients in the study died after unsuccessful coil placement and before they could be re-treated with the open skull clip placement. Thus the article illustrates that GDC""s do not always work, and when they fail they may leave the patient in a critical condition. As illustrated in the article, bleeding during surgical clipping and shortly after the clip placement is also a frequent problem.
From experiences like this, it is apparent that the ultimate goal of intracranial aneurysm treatment is the complete or nearly complete exclusion of the aneurysm cavity from the circulation, which prevents bleeding into the brain cavity and prevents formation of distal blood clots. This goal may be achieved immediately to ensure successful treatment by means of a substantially imperforate stent. It may also be achieved with a slightly perforated stent which alters flow in such a way that compete clotting, over time, is initiated within the aneurysm. It may also be achieved with a perforate stent through which embolic material such as coils are placed in the aneurysm. The treatments may be accomplished by placement of the stents described below which generally do not require the use of balloons for expansion of the stent, so that the blood vessel being treated is not occluded during placement of the stent.
Typically, the stents described below will be delivered percutaneously, introduced into the body through the femoral artery, steered upwardly through the aorta, vena cava, carotid or vertebral artery, and into the various blood vessels of the brain. Further insertion into the brain requires passage through the highly tortuous and small diameter intra-cranial blood vessels. The Circle of Willis, a network of blood vessels which is central to the intracranial vascular system, is characterized by numerous small arteries and bends. Passage of a stent from the internal carotid through the Circle of Willis and into the anterior cerebral artery (for example) requires a turn of about 60xc2x0 through blood vessels of only 1-5 mm in diameter. Clinically, many significant aneurysms take place in the Circle of Willis and approaching blood vessels. The stent and delivery systems described herein are intended for use in such highly tortuous vessels, particularly in the Circle of Willis, the vertebral and carotid siphons and other major blood vessels of the brain. At times, pathologically tortuous vessels may be encountered in the deeper vessels of the brain, and these vessels may be characterized by small diameter, by branching at angles in excess of 90xc2x0 and by inaccessibility with guide wires larger than the standard 0.018 guide-wires. These pathologically tortuous vessels may also be subject to aneurysms and AVM""s which can be treated with the stents described below.
Stents for intra-cranial use are described in detail below. The physical characteristics of prior art balloon expandable stents and self expanding stents make them clearly unsuitable for intra-cranial use, because of their delivery profile and tendency to temporarily occlude the vessel during deployment. They have not been proposed for intra-cranial use. Palmaz stents, Palmaz-Schatz(trademark) stents, Wallstents, Cragg stents, Strecker stents and Gianturco stents and other stents are too rigid to allow placement in the cerebral blood vessels, some require a balloon for deployment, and all are too open to immediately occlude an aneurysm. Presented below are several embodiments of stents suitable for intra-cranial use.
The self expanding rolled sheet stent is suitable for use in the intra-cranial arteries. The rolled sheet is made of Elgiloy(trademark), nitinol, stainless steel, plastic or other suitable material, and is imparted with resilience to urge outward expansion of the roll to bring the rolled stent into contact with the inner wall of a diseased artery. The rolled sheet is adapted for easy insertion and non-deforming radial flexibility to facilitate tracking along the tortuous insertion pathways into the brain. Much of the material of the stent is removed to create a highly perforated stent upon unrolling of the stent within the blood vessel. However, the material is removed in a pattern of perforations that leaves the stent with sufficient hoop strength to open and remain patent in the blood vessel. The unrolled stent may be two or more layers of Elgiloy(trademark), thus providing radial strength for the stent and creating at least a slight compliance mismatch between the stent and the blood vessel, thereby creating a seal between the stent and the blood vessel wall. For placement, the stent is tightly rolled upon or captured within the distal tip of an insertion catheter. The stent can be placed in the intra-cranial blood vessels (arteries and veins) of a patient to accomplish immediate and complete isolation of an aneurysm and side branches from the circulatory system. The stent may be placed across a target site such as an aneurysm neck, origin of a fistula, or branch blood vessels feeding a tumor in order to redirect the flow of blood away from the target. It can be used as a stand alone device which is left in the intra-cranial artery permanently, or it may be used as a temporary device which allows for immediate stabilization of a patient undergoing rupture of a blood vessel an aneurysm or awaiting open skull surgery for clipping or resection of an aneurysm. The stent can be used for stabilization and isolation of a vascular defect during surgery of the vascular defect. Another advantage of this type of stent is that it can be wound down should repositioning be required prior to full release. It is possible to rewind and reposition or remove the device using grasping tools.
The stent described below is designed with perforation patterns which provide a rolled stent having desirable porosity and undercut pores which allow endothelial in-growth into the wall of the stent to assist in anchoring the stent into the blood vessel. The perforations on the unrolled stent are created and placed in sets of wave like patterns as illustrated in the Figures.